Children are uniquely vulnerable to environmental toxins. This heightened susceptibility stems from several sources and is reviewed in detail in the articles by Bearer and by Goldman in this journal issue. To summarize:

Children have greater exposures to environmental toxins than adults. Pound for pound of body weight, children drink more water, eat more food, and breathe more air than adults.4 For example, children in the first six months of life drink seven times as much water per pound as does the average American adult. Children ages one through five years eat three to four times more food per pound than the average adult American. In addition, children have unique food preferences. For example, the average one-year-old drinks 21 times more apple juice and 11 times more grape juice and eats 2 to 7 times more grapes, bananas, pears, carrots, and broccoli than the average adult.4 Moreover, the air intake of a resting infant is twice that of an adult. These patterns of increased consumption reflect the rapid metabolism of children as well as their growth and development. The obvious implication for environmental health is that children will have substantially heavier exposures pound for pound than adults to any toxins that are present in water, food, or air. This has been demonstrated very clearly in the case of children's exposures to pesticides in the diet.4

Two additional characteristics of children further magnify their exposures to toxins in the environment: (1) their hand-to- mouth behavior, which increases their ingestion of any toxins in dust or soil; and (2) their play close to the ground, which increases their exposure to toxins in dust, soil, and carpets as well as to any toxins that form low-lying layers in the air such as certain pesticide vapors.

Children's metabolic pathways, especially in the first months after birth, are immature compared with those of adults. As a consequence of this biochemical immaturity, children's ability to metabolize, detoxify, and excrete certain toxins is different from that of adults. In some instances, children are actually better able than adults to deal with environmental toxins. More commonly, however, they are less able than adults to deal with toxic chemicals and thus are more vulnerable to them.5,6

Children are undergoing rapid growth and development, and their delicate developmental processes are easily disrupted. Many organ systems in young children—the nervous system in particular—undergo very rapid growth and development in the first months and years of life. During this period, structures are developed and vital connections are established. Indeed, development of the nervous system continues all through childhood, as is evidenced by the fact that children continue to acquire new skills progressively as they grow and develop—crawling, walking, talking, reading, and writing. The nervous system is not well able to repair any structural damage that is caused by environmental toxins. Thus, if cells in the developing brain are destroyed by chemicals such as lead, mercury, or solvents, or if vital connections between nerve cells fail to form, there is high risk that the resulting neurobehavioral dysfunction will be permanent and irreversible.7 The consequences can be loss of intelligence and alteration of normal behavior.

Because children have more future years of life than do most adults, they have more time to develop any chronic diseases that may be triggered by early environmental exposures. Many diseases that are triggered by toxins in the environment require decades to develop. Examples include mesothelioma caused by exposure to asbestos, leukemia caused by benzene, breast cancer that may be caused by DDT, and possibly some chronic neurologic diseases such as Parkinson's disease that may be caused by exposures to environmental neurotoxins.8 Many of those diseases are now thought to be the products of multistage processes within the body's cells which require many years to evolve from earliest initiation to actual manifestation of illness. Consequently, certain carcinogenic and toxic exposures sustained early in life appear more likely to lead to disease than the same exposures encountered later in life.4.